In a 4-quart Dutch oven, heat the olive oil over medium heat. Add the onions, leek and garlic and cook, stirring, for 10 minutes or until onions are soft. Add the squash and lemon thyme and cook, stirring for 5 minutes. Increase to medium high heat; add the chicken broth and salt. Cook, partially covered, at a low boil for 20 minutes or until the squash is soft. Discard the thyme.

Puree the soup in batches in a covered blender, then return to the Dutch oven and heat through. Add the lemon juice and hot pepper sauce to taste.